Certain rocks and minerals are characterized by patterns of contrasting pigmentation which appear on cut surfaces. Examples include marble, malachite and opal. These patterns contribute to the aesthetic appeal of these materials and are here termed marbleized.
Many rock and mineral materials which are most appealing and valuable in cut form are either rare or difficult to fabricate by cutting. Consequently attempts have been made to produce articles of manufacture which are imitative of natural materials. Among such articles are those produced on a potter's wheel and having patterns which are applied to the surface of the articles by stamping, brushwork, decals or multicolored glazing. Such articles are not, however, the same as those of natural rocks or minerals nor the same as the articles produced in accordance with this invention.
The patterns on cut surfaces of natural rocks and minerals are the surface traces of three dimensional bodies which are characteristic of each material. These bodies may be folded or undulating laminae or striae or amorphous masses with either sharply defined or diffuse delineation within the rock or mineral.
In the prior art there are methods of obtaining surface patterns, much as on terrazo flooring by grinding and polishing hardened hydraulic cement with aggregate material. The cut sections of such materials reveal the outlines and texture of the aggregate particles which are sharply delineated along a complete perimeter. Although terazzo is imitative of certain natural rocks the surface pattern is not considered to be marbleized in the context of the present invention.
In the prior art there are methods of obtaining a marbleized pattern on ceramic ware by molding non-homogeneous materials on a potter's wheel and, after drying, cutting facets or fluting to expose a faceted or fluted surface with the desired pattern. This method is extremely difficult and laborious, especially on surfaces which are doubly concave or doubly convex. Moreover, it is more satisfying to have most ceramic articles in the conventional rounded form which is characteristic of articles produced on a potter's wheel without additional modification.